CODEWITHSUNDEEP
c++if-statement
Amber Roxanna
Amber Roxanna

Reputation: 1695

if-else statement behaving incorrectly

So i have two functions. one function checks to see if the given sides form a right triangle. The problem is that when I call the function in the if-else statement in classify, I always get "Not a right Triangle" even though the value of isRightTriangle(sides) is true.

bool isRightTriangle(int sides[])
{
    std::sort(sides, sides+3);

    if((pow(sides[0],2) + pow(sides[1],2)) == pow(sides[2],2))
        return true;
    return false;
}

void classify(int sides[], ofstream &outfile)
{
    int largest(int []);
    void typeOfTriangle(int [], ofstream &);
    bool isRightTriangle(int []);

    outfile << "Largest Side: " << largest(sides) << endl;
    typeOfTriangle(sides,outfile);

    if(isRightTriangle(sides))
        outfile << "Right Triangle\n\n\n";
    else
        outfile << "Not a Right Triangle\n\n\n";
}

Upvotes: 0

Views: 219

Answers (2)

Potatoswatter
Potatoswatter

Reputation: 137930

Floating point arithmetic doesn't generally produce perfectly precise results, but == checks for exact equality. Instead of comparing a == b, use abs( a - b ) < precision_limit. This essentially applies to floating-point arithmetic in all languages.

This doesn't explain why it would fail for 3, 4, 5, but there appears to be a lot of code you're not showing us. It would be a very good idea to have isRightTriangle print the numbers it's analyzing before the if.

(By the way, now I see you're passing integers to pow. In this case, imprecise results can only occur for very large numbers, and the precision_limit would be at least one.)

Upvotes: 8

Cogwheel
Cogwheel

Reputation: 23237

As others have mentioned, you're using floating point values and expecting exact results. Since you're only ever squaring the numbers (pow(x, 2)) you should just multiply them together instead. That's usually faster than pow, even for floats, and it works for any type of number.

Upvotes: 2

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